Historical:Sterling Till Member
H. B. Willman and John C. Frye
The Sterling Till Member of the Glasford Formation was informally named the Sterling till (Frye et al., 1969, p. 25) for Sterling, Whiteside County. It is herein formally named a member.
The type section is the Emerson Quarry Section (Frye et al., 1969, p. 34) 2 miles west of Sterling, SE NW SE Sec. 13, T. 21 N., R. 6 E.
It is the uppermost till member of the Glasford in the region north of the Green River Lobe and is similar in clay mineral composition to the Radnor Till Member, which
occupies the same stratigraphic position south of the Green River Lobe.
The upper boundary of the member is the top of the Sangamon Soil, or, locally, the base of the accretion-gley of the Berry Clay Member (e.g., Red Birch School, Coleta Sections, table 7). It is overlain in some places by the Winnebago Formation, the Robein Silt, the Wedron Formation, or the Peoria Loess, and it overlies the Ogle Till Member or older units.
Extent and thickness
The Sterling Member is as much as 40 feet thick in the vicinity of Sterling, but it generally is thinner. The geographic extent of the Sterling Till Member is shown in figure 6.
It has an extremely high illite content. Its typical composition is given in table 2.
Age and correlation
The Sterling Till Member is classed within the Jubileean Substage of the Illinoian Stage.
FRYE, J. C., H. D. GLASS, J. P. KEMPTON, and H. B. WILLMAN, 1969, Glacial tills of northwestern Illinois: Illinois State Geological Survey Circular 437, 47 p.
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